More Fun with Bits

The method below multiplies a float by 2 by manipulating its bits to increment the exponent. See the javadoc for Float.intBitsToFloat() for details on the IEEE754 floating-point representation. Unlike the previous blog entry, the methods used here have been around a long time.

static float multiplyByTwo(float x) {
    // View the float as 32 bits
    int bits = Float.floatToIntBits(x);
    // Extract the bits that represent the exponent
    int exponent = (bits >> 23) & 0xFF;
    // clear the exponent bits
    bits &= ~(0xFF << 23);
    // Increment the exponent and set this new value
    bits |= ((exponent+1) & 0xFF) << 23;
    // Return the bits as a float
    return Float.intBitsToFloat(bits);
}